Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
In some situations, it is difficult to construct a photodiode pixel circuitry that completely resets the photodiode in the low voltage environment that most modern image sensors operate in. Image lag is residual information (image charge) left in a photodiode after the photodiode has been read-out and reset. For example, when the sensor is moving between image frames, image lag may result in ghost images (images of previously captured scenes) in the most recent image output by the image sensor. This is not desirable as ghost images degrade image quality and may confuse machines analyzing the images.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.